The answer is 38, because if you take away the 15 he bought afterwards (34-15) you get 19, and then since he sold half his collection you would double that (19×2) and that's 38.
10
If you treat the number as x, then 
.
(2x + 10)(x - 9)
2x(x - 9) + 10(x - 9)
2x(x) - 2x(9) + 10(x) - 10(9)
2x² - 18x + 10x - 90
2x² - 8x - 90
Case 1: Probabilities cannot add up to a number greater (or less) than 1. This would mean there is greater than a 100% chance of something happening which just doesn't make sense. 0.4 + 0.4 + 0.3 = 1,1
Case 2: You cannot have a negative probability. That is claiming that there is a -10% chance of an event happening, there is at the very least a 0%. Despite them "adding" up to 1, the negative probability makes no sense.
Hope I helped!
Answer: theirs is no question
Step-by-step explanation:
